Method of electroplating photoresist defined features from copper electroplating baths containing reaction products of imidazole compounds, bisepoxides and halobenzyl compounds

ABSTRACT

Electroplating methods enable the plating of photoresist defined features which have substantially uniform morphology. The electroplating methods include copper electroplating baths with reaction products of imidazole compounds, bisepoxides and halobenzyl compounds to electroplate the photoresist defined features. Such features include pillars, bond pads and line space features.

FIELD OF THE INVENTION

The present invention is directed to a method of electroplatingphotoresist defined features from copper electroplating baths whichinclude reaction products of imidazole compounds, bisepoxides andhalobenzyl compounds. More specifically, the present invention isdirected to a method of electroplating photoresist defined features fromcopper electroplating baths which include reaction products of imidazolecompounds, bisepoxides and halobenzyl compounds where the photoresistdefined features have substantially uniform surface morphology.

BACKGROUND OF THE INVENTION

Photoresist defined features include copper pillars and redistributionlayer wiring such as bond pads and line space features for integratedcircuit chips and printed circuit boards. The features are formed by theprocess of lithography where a photoresist is applied to a substratesuch as a semiconductor wafer chip often referred to as a die inpackaging technologies, or epoxy/glass printed circuit boards. Ingeneral, the photoresist is applied to a surface of the substrate and amask with a pattern is applied to the photoresist. The substrate withthe mask is exposed to radiation such as UV light. Typically thesections of the photoresist which are exposed to the radiation aredeveloped away or removed exposing the surface of the substrate.Depending on the specific pattern of the mask an outline of a circuitline or aperture may be formed with the unexposed photoresist left onthe substrate forming the walls of the circuit line pattern orapertures. The surface of the substrate includes a metal seed layer orother conductive metal or metal alloy material which enables the surfaceof the substrate conductive. The substrate with the patternedphotoresist is then immersed in a metal electroplating bath, typically acopper electroplating bath, and metal is electroplated in the circuitline pattern or aperture to form features such as pillars, bond pads orcircuit lines, i.e., line space features. When electroplating iscomplete, the remainder of the photoresist is stripped from thesubstrate with a stripping solution and the substrate with thephotoresist defined features is further processed.

Pillars, such as copper pillars, are typically capped with solder toenable adhesion as well as electrical conduction between thesemiconductor chip to which the pillars are plated and a substrate. Sucharrangements are found in advanced packaging technologies. Solder cappedcopper pillar architectures are a fast growing segment in advancedpackaging applications due to improved input/output (I/O) densitycompared to solder bumping alone. A copper pillar bump with thestructure of a non-reflowable copper pillar and a reflowable solder caphas the following advantages: (1) copper has low electrical resistanceand high current density capability; (2) thermal conductivity of copperprovides more than three times the thermal conductivity of solder bumps;(3) can improve traditional BGA CTE (ball grid array coefficient ofthermal expansion) mismatch problems which can cause reliabilityproblems; and (4) copper pillars do not collapse during reflow allowingfor very fine pitch without compromising stand-off height.

Of all the copper pillar bump fabrication processes, electroplating isby far the most commercially viable process. In the actual industrialproduction, considering the cost and process conditions, electroplatingoffers mass productivity and there is no polishing or corrosion processto change the surface morphology of copper pillars after the formationof the copper pillars. Therefore, it is particularly important to obtaina smooth surface morphology by electroplating. The ideal copperelectroplating chemistry and method for electroplating copper pillarsyields deposits with excellent uniformity, flat pillar shape andvoid-free intermetallic interface after reflow with solder and is ableto plate at high deposition rates to enable high wafer through-out.However, development of such plating chemistry and method is a challengefor the industry as improvement in one attribute typically comes at theexpense of another. Copper pillar based structures have already beenemployed by various manufacturers for use in consumer products such assmart phones and PCs. As Wafer Level Processing (WLP) continues toevolve and adopt the use of copper pillar technology, there will beincreasing demand for copper plating baths and methods with advancedcapabilities that can produce reliable copper pillar structures.

Similar problems of morphology are also encountered with the metalelectroplating of redistribution layer wiring. Defects in the morphologyof bond pads and line space features also compromise the performance ofadvanced packaging articles. Accordingly, there is a need for a copperelectroplating methods and chemistries which provide copper photoresistdefined features where the features have substantially uniform surfacemorphology.

SUMMARY OF THE INVENTION

A method including: a) providing a substrate comprising a layer ofphotoresist, wherein the layer of photoresist comprises a plurality ofapertures; b) providing a copper electroplating bath comprising one ormore reaction products of one or more imidazole compounds, one or morebisepoxides and one or more halobenzyl compounds; an electrolyte; one ormore accelerators; and one or more suppressors; c) immersing thesubstrate comprising the layer of photoresist with the plurality ofapertures in the copper electroplating bath; and d) electroplating aplurality of copper photoresist defined features in the plurality ofapertures, the plurality of photoresist defined features comprise anaverage % TIR of 5% to 10%.

Copper electroplating baths include a reaction product of one or moreimidazole compounds, one or more bisepoxides and one or more halobenzylcompounds, a electrolyte, one or more sources of copper ions, one ormore accelerators and one or more suppressors in sufficient amounts toelectroplate copper photoresist defined features having an average % TIRof 5% to 10%.

The present invention is also directed to an array of photoresistdefined features on a substrate comprising an average % TIR of 5% to 10%and a % WID of 8% to 10%.

The copper electroplating methods and baths provide copper photoresistdefined features which have a substantially uniform morphology and aresubstantially free of nodules. The copper pillars and bond pads have asubstantially flat profile. The copper electroplating baths and methodsenable an average % TIR to achieve the desired morphology.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a SEM of a copper pillar at 300 X electroplated from a copperelectroplating bath containing a reaction product of 1H-imidazole,1,4-butanediol diglycidyl ether and 1,4-bis(chloromethyl) benzene.

FIG. 2 is a SEM of a copper pillar at 300 X electroplated from a copperelectroplating bath containing a conventional leveler compound which isa reaction product of 2-methylquinolin-4-amine, 2-(2-aminoethyl)pyridineand 1,4-butanediol diglycidyl ether.

DETAILED DESCRIPTION OF THE INVENTION

As used throughout this specification the following abbreviations shallhave the following meanings unless the context clearly indicatesotherwise: A=amperes; A/dm²=amperes per square decimeter=ASD; °C.=degrees Centigrade; UV=ultraviolet radiation; g=gram; ppm=parts permillion=mg/L; L=liter, μm=micron=micrometer; mm=millimeters;cm=centimeters; DI=deionized; mL=milliliter; mol=moles; mmol=millimoles;Mw=weight average molecular weight; Mn=number average molecular weight;SEM=scanning electron microscope; FIB=focus ion beam; WID=within-die;TIR=total indicated runout=total indicator reading=full indicatormovement=FIM; RDL=redistribution layer; and Avg.=average.

As used throughout this specification, the term “plating” refers tometal electroplating. “Deposition” and “plating” are usedinterchangeably throughout this specification. “Accelerator” refers toan organic additive that increases the plating rate of theelectroplating bath. “Suppressor” refers to an organic additive thatsuppresses the plating rate of a metal during electroplating. The term“array” means an ordered arrangement. The term “moiety” means a part ofa molecule or polymer that may include either whole functional groups orparts of functional groups as substructures. The terms “moiety” and“group” are used interchangeably throughout the specification. The term“aperture” means opening, hole or gap. The term “morphology” means theform, shape and structure of an article. The term “total indicatorrunout” or “total indicator reading” is the difference between themaximum and minimum measurements, that is, readings of an indicator, onplanar, cylindrical, or contoured surface of a part, showing its amountof deviation from flatness, roundness (circularity), cylindricity,concentricity with other cylindrical features or similar conditions. Theterm “profilometry” means the use of a technique in the measurement andprofiling of an object or the use of a laser or white lightcomputer-generated projections to perform surface measurements of threedimensional objects. The term “pitch” means a frequency of featurepositions from each other on a substrate. The term “normalizing” means arescaling to arrive at values relative to a size variable such as aratio as % TIR. The term “average” means a number expressing the centralor typical value of a parameter. The term “parameter” means a numericalor other measurable factor forming one of a set that defines a system orsets the conditions of its operations. The articles “a” and “an” referto the singular and the plural.

All numerical ranges are inclusive and combinable in any order, exceptwhere it is clear that such numerical ranges are constrained to add upto 100%.

Methods and baths for electroplating copper photoresist defined featuresof the present invention enable an array of photoresist defined featureshaving an average % TIR such that the features have a morphology whichis substantially smooth, free of nodules and with respect to pillars,bond pads and line space features have substantially flat profiles. Thephotoresist defined features of the present invention are electroplatedwith photoresist remaining on the substrate and extend beyond the planeof the substrate. This is in contrast to dual damascene and printedcircuit board plating which typically do not use photoresist to definefeatures which extend beyond the plane of the substrate but are inlaidinto the substrate. An important difference between photoresist definedfeatures and damascene and printed circuit board features is that withrespect to the damascene and printed circuit boards the plating surfaceincluding the sidewalls are all conductive. The dual damascene andprinted circuit board plating baths have a bath formulation thatprovides bottom-up or super-conformal filling, with the bottom of thefeature plating faster than the top of the feature. In photoresistdefined features, the sidewalls are non-conductive photoresist andplating only occurs at the feature bottom with the conductive seed layerand proceeds in a conformal or same plating speed everywhere deposition.

While the present invention is substantially described with respect tomethods of electroplating copper pillars having a circular morphology,the present invention also applies to other photoresist defined featuressuch as bond pads and line space features. In general, the shapes of thefeatures may be, for example, oblong, octagonal and rectangular inaddition to circular or cylindrical. The methods of the presentinvention are preferably for electroplating copper cylindrical pillars.

The copper electroplating methods provide an array of copper photoresistdefined features, such as copper pillars, with an average % TIR of 5% to10%.

In general, the average % TIR for an array of photoresist definedfeatures on a substrate involves determining the % TIR of individualfeatures from the array of features on the single substrate andaveraging them. Typically, the average % TIR is determined bydetermining the % TIR for individual features of a region of low densityor larger pitch and the % TIR for individual features of a region ofhigh density or smaller pitch on the substrate and averaging the values.By measuring the % TIR of a variety of individual features, the average% TIR becomes representative of the whole substrate.

The % TIR may be determined by the following equation:

% TIR=[height_(center)−height_(edge)]/height_(max)×100

where height_(center) the height of a pillar as measured along itscenter axis and height_(edge) is the height of the pillar as measuredalong its edge at the highest point on the edge. Height_(max) is theheight from the bottom of the pillar to its highest point on its top.Height_(max) is a normalizing factor.

Individual feature TIRs may be determined by the following equation:

TIR=height_(center)−height_(edge),

where height_(center) and height_(edge) are as defined above.

In addition, the copper electroplating methods and baths may provide anarray of copper photoresist defined features with a % WID of 8% to 10%,preferably from 9% to 10%. The % WID or within-die may be determined bythe following equation:

% WID=½×[(height_(max)−height_(min))/height_(avg)]×100

where height_(max) is the height of the tallest pillar of an array ofpillars electroplated on a substrate as measured at the tallest part ofthe pillar. Height_(min) is the height of the shortest pillar of anarray of pillars electroplated on the substrate as measured at thetallest part of the pillar. Height_(avg) is the average height of all ofthe pillars electroplated on the substrate.

Most preferably, the methods of the present invention provide an arrayof photoresist defined features on a substrate where there is a balancebetween the average % TIR and % WID such that the average % TIR rangesfrom 5% to 10% and the % WID ranges from 8% to 10% with the preferredrange as disclosed above.

The parameters of the pillars for determining TIR, % TIR and % WID maybe measured using optical profilometry such as with a white light LEICADCM 3D or similar apparatus. Parameters such as pillar height and pitchmay be measured using such devices.

In general, the copper pillars electroplated from the copperelectroplating baths may have aspect ratios of 3:1 to 1:1 or such as 2:1to 1:1. RDL type structure may have aspect ratios as large as 1:20(height:width).

Preferably the imidazole compounds have the following general formula:

where R₁, R₂ and R₃ are independently chosen from hydrogen, linear orbranched (C₁-C₁₀)alkyl; hydroxyl; linear or branched alkoxy; linear orbranched hydroxy(C₁-C₁₀)alkyl; linear or branched alkoxy(C₁-C₁₀)alkyl;linear or branched, carboxy(C₁-C₁₀)alkyl; linear or branchedamino(C₁-C₁₀)alkyl; substituted or unsubstituted phenyl where thesubstituents may be hydroxyl, hydroxy(C₁-C₃)alkyl, or (C₁-C₃)alkyl.Preferably, R₁, R₂ and R₃ are independently chosen from hydrogen; linearor branched (C₁-C₅)alkyl; hydroxyl; linear or branchedhydroxy(C₁-C₅)alkyl; and linear or branched amino(C₁-C₅)alkyl. Morepreferably R₁, R₂ and R₃ are independently chosen from hydrogen atom and(C₁-C₃)alky such as methyl, ethyl and propyl moieties. Examples of suchcompounds are 1H-imidazole, 2-methylimidazole, 2-isopropylimidazole,2-butyl-5-hydroxymethylimidazole, 2,5-dimethyl-1H-imidazole,2-ethylimidazole and 4-phenylimidazole.

Preferably bisepoxides have a formula:

where R₄ and R₅ are independently chosen from hydrogen and (C₁-C₄)alkyl;R₆ and R₇ are independently chosen from hydrogen, methyl and hydroxyl;m=1-6 and n=1-20 . Preferably, R₄ and R₅ are hydrogen. Preferably R₆ andR₇ are independently chosen from hydrogen, methyl and hydroxyl. Morepreferably R₆ is hydrogen, and R₇ is hydrogen or hydroxyl. When R₇ ishydroxyl and m=2-4, it is preferred that only one R₇ is hydroxyl withthe rest hydrogen. Even more preferably R₆ and R₇ are hydrogen.Preferably m=2-4 and n=1-2. More preferably m=3-4 and n=1.

Compounds of formula (II) include, but are not limited to,1,4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether,di(ethylene glycol) diglycidyl ether, glycerol diglycidyl ether,neopentyl glycol diglycidyl ether, 1,3-butandiol diglycidyl ether,propylene glycol diglycidyl ether, di(propylene glycol) diglycidylether, poly(ethylene glycol) diglycidyl ether compounds andpoly(propylene glycol) diglycidyl ether compounds.

Additional preferred bisepoxides include bisepoxides having cycliccarbon moieties such as those having six carbon cyclic moieties. Suchbisepoxides include, but are not limited to 1,4-cyclohexanedimethanoldiglycidyl ether and resorcinol diglycidyl ether.

Preferably the cyclic halogen compounds are chosen from aromatic halogencompounds having a formula:

where R₈, R₉, R₁₀, R₁₁, R₁₂ and R₁₃ are independently chosen fromhydrogen, linear or branched (C₁-C₁₀)alkyl halide, and linear orbranched (C₁-C₁₀)alkyl with the proviso that at least two of R₈, R₉,R₁₀, R₁₁, R₁₂ and R₁₃ are alkyl halide in the same instance and with theproviso that R₆, R₁₀, and R₁₂, or R₉, R₁₁ and R₁₃ are not methyl groupsin the same instance. Preferably, R₈, R₉, R₁₀, R₁₁, R₁₂ and R₁₃ areindependently chosen from hydrogen, linear or branched (C₁-C₁₀)alkylhalide, and linear or branched (C₁-C₁₀)alkyl with the proviso that atleast two of R₈, R₉, R₁₀, R₁₁, R₁₂ and R₁₃ are alkyl halide in the sameinstance and with the proviso that R₆, R₁₀, and R₁₂, or R₉, R₁₁ and R₁₃are not methyl groups in the same instance. Preferably R₈, R₉, R₁₀, R₁₁,R₁₂ and R₁₃ are independently chosen from hydrogen, linear or branched(C₁-C₅)alkyl halide, and linear or branched (C₁-C₅)alkyl with theproviso that at least two of R₈, R₉, R₁₀, R₁₁, R₁₂ and R₁₃ are alkylhalide in the same instance and with the proviso that R₆, R₁₀, and R₁₂,or R₉, R₁₁ and R₁₃ are not methyl groups in the same instance. Morepreferably R₈, R₁₁, R₁₂ are hydrogen, R₉, R₁₀ and R₁₃ are independentlychosen from hydrogen and (C₁-C₂)alkyl halide with the proviso that atleast two of R₉, R₁₀ and R₁₃ are (C₁-C₂)alkyl halide. Such compoundsinclude, but are not limited to 2,3-bis(chloromethyl)-benezene and1,4-bis(chloromethyl)benzene.

The order of addition of reactants to a reaction vessel may vary,however, preferably, one or more imidazole compounds are dissolved inisopropanol at 80° C. with dropwise addition of one or more bisepoxides.The temperature of the heating bath is then increased from 80° C. to 95°C. Heating with stirring is done for 2 hours to 3 hours. One or morehalobenzyls is then added to the reaction flask and heating is continuedfor 1 hour to 3 hours. The temperature of the heating bath is thenreduced to room temperature with stirring for 4 hours to 8 hours. Theamounts for each component may vary but, in general, sufficient amountof each reactant is added to provide a product where the molar ratio ofthe moiety from the imidazole compound to the moiety from the bisepoxideto the moiety from the halobenzyl ranges from 2-1:0.1-1:0.01-0.5 basedon compound molar ratios.

The aqueous copper electroplating baths contain a source of metal ions,an electrolyte, and a reaction product of one or more imidazolecompounds, one or more bisepoxides and one or more halobenzyls. Theaqueous copper electroplating baths also include an accelerator, asuppressor and optionally a source of halide ions. Metals which may beelectroplated from the baths to form copper pillars include copper andcopper/tin alloy. Preferably copper metal is electroplated.

Suitable copper ion sources are copper salts and include withoutlimitation: copper sulfate; copper halides such as copper chloride;copper acetate; copper nitrate; copper tetrafluoroborate; copperalkylsulfonates; copper aryl sulfonates; copper sulfamate; copperperchlorate and copper gluconate. Exemplary copper alkane sulfonatesinclude copper (C₁-C₆)alkane sulfonate and more preferably copper(C₁-C₃)alkane sulfonate. Preferred copper alkane sulfonates are coppermethanesulfonate, copper ethanesulfonate and copper propanesulfonate.Exemplary copper arylsulfonates include, without limitation, copperbenzenesulfonate and copper p-toluenesulfonate. Mixtures of copper ionsources may be used. One or more salts of metal ions other than copperions may be added to the present electroplating baths. Preferably, thecopper salt is present in an amount sufficient to provide an amount ofcopper ions of 30 to 60 g/L of plating solution. More preferably theamount of copper ions is from 40 to 50 g/L.

The electrolyte useful in the present invention may be alkaline oracidic. Preferably the electrolyte is acidic. Preferably, the pH of theelectrolyte is<2. Suitable acidic electrolytes include, but are notlimited to, sulfuric acid, acetic acid, fluoroboric acid, alkanesulfonicacids such as methanesulfonic acid, ethanesulfonic acid, propanesulfonicacid and trifluoromethane sulfonic acid, aryl sulfonic acids such asbenzenesulfonic acid, p-toluenesulfonic acid, sulfamic acid,hydrochloric acid, hydrobromic acid, perchloric acid, nitric acid,chromic acid and phosphoric acid. Mixtures of acids may beadvantageously used in the present metal plating baths. Preferred acidsinclude sulfuric acid, methanesulfonic acid, ethanesulfonic acid,propanesulfonic acid, hydrochloric acid and mixtures thereof. The acidsmay be present in an amount in the range of 1 to 400 g/L. Electrolytesare generally commercially available from a variety of sources and maybe used without further purification.

Such electrolytes may optionally contain a source of halide ions.Typically chloride ions and bromide ions are used. Exemplary chlorideion sources include copper chloride, tin chloride, sodium chloride,potassium chloride and hydrochloric acid. Sources of bromide ionsinclude sodium bromide, potassium bromide and hydrogen bromide. A widerange of halide ion concentrations may be used in the present invention.Typically, the halide ion concentration is in the range of 0 to 100 ppmbased on the plating bath preferably 50 ppm to 80 ppm. Such halide ionsources are generally commercially available and may be used withoutfurther purification.

The plating compositions typically contain an accelerator. Anyaccelerators (also referred to as brightening agents) are suitable foruse in the present invention. Such accelerators are well-known to thoseskilled in the art. Accelerators include, but are not limited to,N,N-dimethyl-dithiocarbamic acid-(3-sulfopropyl)ester;3-mercapto-propylsulfonic acid-(3-sulfopropyl)ester;3-mercapto-propylsulfonic acid sodium salt; carbonicacid,dithio-O-ethylester-S-ester with 3-mercapto-1-propane sulfonic acidpotassium salt; bis-sulfopropyl disulfide; bis-(sodiumsulfopropyl)-disulfide; 3-(benzothiazolyl-S-thio)propyl sulfonic acidsodium salt; pyridinium propyl sulfobetaine;1-sodium-3-mercaptopropane-1-sulfonate; N,N-dimethyl-dithiocarbamicacid-(3-sulfoethyl)ester; 3-mercapto-ethyl propylsulfonicacid-(3-sulfoethyl)ester; 3-mercapto-ethylsulfonic acid sodium salt;carbonic acid-dithio-O-ethylester-S-ester with 3-mercapto-1-ethanesulfonic acid potassium salt; bis-sulfoethyl disulfide;3-(benzothiazolyl-S-thio)ethyl sulfonic acid sodium salt; pyridiniumethyl sulfobetaine; and 1-sodium-3-mercaptoethane-1-sulfonate.Accelerators may be used in a variety of amounts. In general,accelerators are used in an amount in a range of 0.1 ppm to 1000 ppm.

Suitable suppressors include, but are not limited to, polypropyleneglycol copolymers and polyethylene glycol copolymers, including ethyleneoxide-propylene oxide (“EO/PO”) copolymers and butyl alcohol-ethyleneoxide-propylene oxide copolymers. The weight average molecular weight ofthe suppressors may range from 800-15000, preferably from 1000 to15,000. When such suppressors are used, they are preferably present in arange of 0.5 g/L to 15 g/L based on the weight of the composition, andmore preferably from 1 g/L to 5 g/L.

In general, the reaction products have a number average molecular weight(Mn) of 200 to 125,000, typically from 1000 to 75,000, preferably from1500 to 10,000, although reaction products having other Mn values may beused. Such reaction products may have a weight average molecular weight(Mw) value in the range of 1000 to 500,000, typically from 10,000 to30,000, although other Mw values may be used.

The amount of the reaction product used in the copper electroplatingbaths for plating photoresist defined features, preferably copperpillars, may range from 0.25 ppm to 20 ppm, preferably from 0.25 ppm to10 ppm, more preferably from 0.25 ppm to 5 ppm and even more preferablyfrom 0.25 ppm to 2 ppm, based on the total weight of the plating bath.

The electroplating baths may be prepared by combining the components inany order. It is preferred that the inorganic components such as sourceof metal ions, water, electrolyte and optional halide ion source arefirst added to the bath vessel, followed by the organic components suchas leveling agent, accelerator, suppressor, and any other organiccomponent.

The aqueous copper electroplating baths may optionally contain aconventional leveling agent provided such the leveling agent does notsubstantially compromise the morphology of the copper features. Suchleveling agents may include those disclosed in U.S. Pat. Nos. 6,610,192to Step et al., 7,128,822 to Wang et al., 7,374,652 to Hayashi et al.and 6,800,188 to Hagiwara et al. However, it is preferred that suchleveling agents are excluded from the baths.

Typically, the plating baths may be used at any temperature from 10 to65° C. or higher. Preferably, the temperature of the plating compositionis from 15 to 50° C. and more preferably from 20 to 40° C.

In general, the copper electroplating baths are agitated during use. Anysuitable agitation method may be used and such methods are well-known inthe art. Suitable agitation methods include, but are not limited to: airsparging, work piece agitation, and impingement.

Typically, a substrate is electroplated by contacting the substrate withthe plating bath. The substrate typically functions as the cathode. Theplating bath contains an anode, which may be soluble or insoluble.Potential is applied to the electrodes. Current densities may range from0.25 ASD to 40 ASD, preferably 1 ASD to 20 ASD, more preferably from 4ASD to 18 ASD.

While the method of the present invention may be used to electroplatephotoresist defined features such as pillars, bonding pads and linespace features, the method is described in the context of plating copperpillars which is the preferred feature of the present invention.Typically, the copper pillars may be formed by first depositing aconductive seed layer on a substrate such as a semiconductor chip ordie. The substrate is then coated with a photoresist material and imagedto selectively expose the photoresist layer to radiation such as UVradiation. The photoresist layer may be applied to a surface of thesemiconductor chip by conventional processes known in the art. Thethickness of the photoresist layer may vary depending on the height ofthe features. Typically the thickness ranges from 1 μm to 250 μm. Apatterned mask is applied to a surface of the photoresist layer. Thephotoresist layer may be a positive or negative acting photoresist. Whenthe photoresist is positive acting, the portions of the photoresistexposed to the radiation are removed with a developer such as analkaline developer. A pattern of a plurality of apertures is formed onthe surface which reaches all the way down to the seed layer on thesubstrate or die. The pitch of the pillars may range from 20 μm to 400μm. Preferably the pitch may range from 40 μm to 250 μm. The diametersof the apertures may vary depending on the diameter of the feature. Thediameters of the apertures may range from 2 μm to 200 μm, typically from10 μm to 75 μm. The entire structure may then be placed in a copperelectroplating bath containing one or more of the reaction products ofthe present invention. Electroplating is done to fill at least a portionof each aperture with a copper pillar with a substantially flat top.Electroplating is vertical fill without horizontal or superfilling. Theentire structure with the copper pillars is then transferred to a bathcontaining solder, such as a tin solder or tin alloy solder such as atin/silver or tin/lead alloy and a solder bump is electroplated on thesubstantially flat surface of each copper pillar to fill portions of theapertures. The remainder of the photoresist is removed by conventionalmeans known in the art leaving an array of copper pillars with solderbumps on the die. The remainder of the seed layer not covered by pillarsis removed through etching processes well known in the art. The copperpillars with the solder bumps are placed in contact with metal contactsof a substrate such as a printed circuit board, another wafer or die oran interposer which may be made of organic laminates, silicon or glass.The solder bumps are heated by conventional processes known in the artto reflow the solder and join the copper pillars to the metal contactsof the substrate. Conventional reflow processes for reflowing solderbumps may be used. An example of a reflow oven is FALCON 8500 tool fromSikiama International, Inc. which includes 5 heating and 2 coolingzones. Reflow cycles may range from 1-5. The copper pillars are bothphysically and electrically contacted to the metal contacts of thesubstrate. An underfill material may then be injected to fill spacebetween the die, the pillars and the substrate. Conventional underfillswhich are well known in the art may be used.

FIG. 1 is a SEM of a copper pillar of the present invention havingcylindrical morphology with a base and sufficiently flat top forelectroplating solder bumps. During reflow solder is melted to obtain asmooth surface. If pillars are too domed during reflow, the solder maymelt and flow off the sides of the pillar and then there is not enoughsolder on the top of the pillar for subsequent bonding steps. If thepillar is too dished as shown in FIG. 2, material left from the copperbath which was used to electroplate the pillar may be retained in thedished top and contaminate the solder bath, thus shortening the life ofthe solder bath.

To provide a metal contact and adhesion between the copper pillars andthe semiconductor die during electroplating of the pillars, an underbumpmetallization layer typically composed of a material such as titanium,titanium-tungsten or chromium is deposited on the die. Alternatively, ametal seed layer, such as a copper seed layer, may be deposited on thesemiconductor die to provide metal contact between the copper pillarsand the semiconductor die. After the photosensitive layer has beenremoved from the die, all portions of the underbump metallization layeror seed layer are removed except for the portions underneath thepillars. Conventional processes known in the art may be used.

While the height of the copper pillars may vary, typically they range inheight from 1 μm to 200 μm, preferably from 5 μm to 50 μm, morepreferably from 15 μm to 50 μm. Diameters of the copper pillars may alsovary. Typically the copper pillars have a diameter of 2 μm to 200 μm,preferably from 10 μm to 75 μm, more preferably 20 μm to 25 μm.

The copper electroplating methods and baths provide copper photoresistdefined features which have a substantially uniform morphology and aresubstantially free of nodules. The copper pillars and bond pads have asubstantially flat profile. The copper electroplating baths and methodsenable an average % TIR to achieve the desired morphology.

The following examples are intended to further illustrate the inventionbut are not intended to limit its scope.

EXAMPLE 1

Imidazole (100 mol) was dissolved in 20 mL isopropanol in a 100 mLround-bottom, three-neck flask equipped with condenser, thermometer, andstir bar at 80° C. 1,4-butanediol diglycidyl ether (30 mmol) was addeddropwise to the solution, and the vial containing the 1,4-butanedioldiglycidyl ether was rinsed with 2 mL isopropanol. The heating bathtemperature was increased to 95° C. The resulting mixture was heated for2.5 hours and 1,4-bis(chloromethyl) benzene (30 mmol) was added as asolid to the reaction mixture and rinsed down the sides of the flaskwith 2 mL isopropanol. The oil bath temperature was kept at 95° C. for 2hours, and then the reaction was left to stir at room temperatureovernight. The reaction mixture was rinsed with water into apolyethylene bottle for storage. The molar ratio of imidazole moiety to1,4-butanediol diglycidyl ether to 1,4-bis(chloromethyl) benzene was1:0.3:0.3 based on monomer molar ratios. Reaction product 1 was usedwithout purification.

EXAMPLE 2

Imidazole (100 mmol) was dissolved in 20 mL isopropanol in a 100 mLround-bottom, three-neck flask equipped with condenser, thermometer, andstir bar at 80° C. 1,4-butanediol diglycidyl ether (30 mmol) was addeddropwise to the solution, and the vial containing the 1,4-butanedioldiglycidyl ether was rinsed with 2 mL isopropanol. The heating bathtemperature was increased to 95° C. The resulting mixture was heated for2.25 hours and 1,2-bis(chloromethyl) benzene (30 mmol) was added as asolid to the reaction mixture and rinsed down the sides of the flaskwith 2 mL isopropanol. The oil bath temperature was kept at 95° C. for 2hours, and then the reaction was left to stir at room temperatureovernight. The reaction mixture was rinsed with water into apolyethylene bottle for storage. The molar ratio of imidazole moiety to1,4-butanediol diglycidyl ether to 1,2-bis(chloromethyl)benzene was1:0.3:0.3 based on monomer molar ratios. Reaction product 2 was usedwithout purification.

EXAMPLE 3

An aqueous acid copper electroplating bath was prepared by combining 40g/L copper ions from copper sulfate pentahydrate, 140 g/L sulfuric acid,50 ppm chloride ion, 5 ppm of an accelerator and 2 g/L of a suppressor.The accelerator was bis(sodium-sulfopropyl)disulfide. The suppressor wasan EO/PO copolymer having a weight average molecular weight of 1,000 andterminal hydroxyl groups. The electroplating bath also contained 1 ppmof reaction product 1 from Example 1. The pH of the bath was less than1.

A 300 mm silicon wafer segment with a patterned photoresist 50 μm thickand a plurality of apertures (available from IMAT, Inc., Vancouver,Wash.) was immersed in the copper electroplating bath. The anode was asoluble copper electrode. The wafer and the anode were connected to arectifier and copper pillars were electroplated on the exposed seedlayer at the bottom of the apertures. The aperture diameters were 50 μm.Current density during plating was 9 ASD and the temperature of thecopper electroplating bath was at 25° C. After electroplating theremaining photoresist was then stripped with BPR photostripper solutionavailable from the Dow Chemical Company leaving an array of copperpillars on the wafer. Eight copper pillars were then analyzed for theirmorphology. The heights and TIR of the pillars were measured using anoptical white light LEICA DCM 3D microscope. The % TIR was determined bythe following equations:

% TIR=[height_(center)−height_(edge)]/height_(max)×100,

TIR=height_(center)−height_(edge)

The average % TIR of the eight pillars was also determined as shown inthe table.

TABLE 1 Pillar Height_(max) Pillar TIR Pillar # Pitch (μm) (μm) (μm) %TIR 1 100 34.8 3.5 10.0 2 100 32.0 3.5 10.9 3 100 32.0 3.3 10.3 4 10032.5 3.6 11.1 5 100 35.0 3.6 10.3 6 250 38.9 3.5 9.0 7 250 37.9 2.8 7.48 250 36.9 3.4 9.2 Avg. — 35.0 3.4 9.7%

The % WID for the array of pillars was determined with the optical whitelight LEICA DCM 3D microscope and the following equation:

% WID=½×[(height_(max)−height_(min))/height_(avg)]×100

The % WID was 9.8% and the average % TIR was 9.7%. The surface of thepillars all appeared smooth and free of nodules. The copperelectroplating bath which included reaction product 1 plated very goodcopper pillars. FIG. 1 is a 300X AMRAY SEM image of one of the pillarsplated on a seed layer and analyzed with the optical microscope. Thesurface morphology was smooth and although the pillar had a slight dome,it was sufficiently flat on top for receiving solder.

EXAMPLE 4

The method of Example 3 was repeated except that the reaction productwas reaction product 2 from Example 2. The silicon wafer, copperelectroplating bath and plating conditions were the same. ReactionProduct 2 was included in the bath in the amount of 1 ppm. After theplating was completed the photoresist was stripped from the wafer withan alkaline stripping solution leaving an array of copper pillars. Eightcopper pillars were then analyzed for their morphology.

TABLE 2 Pillar Height_(max) Pillar TIR Pillar # Pitch (μm) (μm) (μm) %TIR 1 100 34.5 2.1 6.1 2 100 31.2 2.2 7.0 3 100 31.3 2.1 6.7 4 100 32.11.9 5.9 5 100 35.0 1.6 4.6 6 250 38.1 1.3 3.4 7 250 36.8 0.9 2.4 8 25035.2 1.3 3.7 Avg. — 34.3 1.7 5.0All of the pillars were smooth. The % WID was determined to be 10.1% andthe average % TR was determined to be 5.0%. The array of pillars hadsubstantially flat tops suitable for receiving solder.

EXAMPLE 5

A 300 mm silicon wafer segment with a patterned photoresist 50 μm thickand a plurality of vias 50 μm in diameter (available from IMAT, Inc.,Vancouver, Wash.) was immersed in the copper electroplating bath ofExample 3. The anode was a soluble copper electrode. The wafer and theanode were connected to a rectifier and copper pillars wereelectroplated on the exposed seed layer at the bottom of the vias.Current density during plating was 9 ASD and the temperature of thecopper electroplating bath was at room temperature.

After the wafer was plated with copper pillars, the tops of the copperpillars were then electroplated with a tin/silver solder using SOLDERON™BP TS6000 tin/silver electroplating solution (available from the DowChemical Company, Midland, Mich.). The solder was electroplated up tothe level of the photoresist in each aperture. The photoresist was thenstripped using an alkaline stripper. The silicon wafers were thenreflowed using a Falcon 8500 tool from Sikama International, Inc. having5 heating and 2 cooling zones using temperatures of 140/190/230/230/260°C., with a 30 second dwell time and a conveyor rate of 100 cm/minute anda nitrogen flow rate of 40 cubic feet/hour (approximately 1.13 cubicmeters/hour). ALPA 100-40 flux (Cookson Electronics, Jersey City, N.J.,U.S.A) was the flux used in the reflow. One reflow cycle was done. Afterreflow the eight pillars were cross sectioned using a FIB-SEM and theinterface between the copper pillars and the solder were examined forvoids. There were no observable voids, thus there was good adhesionbetween the solder and the copper pillars.

EXAMPLE 6

The method described in Example 5 was repeated except that the copperelectroplating bath included reaction product 2 instead of reactionproduct 1. There were no observable voids at the interface between thecopper and the solder, thus there was good adhesion between the solderand the copper pillars.

EXAMPLE 7 (Comparative)

In a 125 mL round-bottom, three-neck flask equipped with a condenser anda thermometer, 90 mmol of 2-methylquinolin-4-amine, 10 mmol of2-(2-aminoethyl)pyridine were added into a mixture of 20 mL of DI waterand 5 ml of 50% sulfuric acid. The mixture was heated to 80° C. followedby drop wise addition of 100 mmol of 1,4-butanediol diglycidyl ether.The resulting mixture was heated for about 4 hours using an oil bath setto 95° C. and then left to stir at room temperature for an additional 8hours. The reaction product (reaction product 3-comparative) was dilutedusing acidified water and used without further purification.

EXAMPLE 8 (Comparative)

The method described in Example 3 was repeated with the same copperelectroplating bath, wafer and plating parameters except reactionproduct 3-comparative was substituted for reaction product 1. Reactionproduct 3-comparative was included in the copper electroplating bath inan amount of 1 ppm. After the wafer was plated with pillars, thephotoresist was stripped leaving an array of copper pillars on thesilicon wafer. The pillars appeared rough and many had “sink-hole”centers as shown in FIG. 2. The % WID and average % TIR were notcalculated. The pillars were very defective, thus the profilometer wasunable to read them accurately.

What is claimed is:
 1. A method comprising: a) providing a substratecomprising a layer of photoresist, wherein the layer of photoresistcomprises a plurality of apertures; b) providing a copper electroplatingbath comprising one or more reaction products of one or more imidazolecompounds, one or more bisepoxides and one or more halobenzyl compounds;an electrolyte; one or more accelerators; and one or more suppressors;c) immersing the substrate comprising the layer of photoresist with theplurality of apertures in the copper electroplating bath; and d)electroplating a plurality of copper photoresist defined features in theplurality of apertures, the plurality of photoresist defined featurescomprise an average % TIR of 5% to 10%.
 2. The method of claim 1,wherein a % WID of the plurality of photoresist defined features is from8% to 10%.
 3. The method of claim 1, wherein the one or more imidazolecompounds have a formula:

where R₁, R₂ and R₃ may be the same or different and chosen fromhydrogen atom, linear or branched (C₁-C₁₀)alkyl; hydroxyl; linear orbranched alkoxy; linear or branched hydroxy(C₁-C₁₀)alkyl; linear orbranched alkoxy(C₁-C₁₀)alkyl; linear or branched, carboxy(C₁-C₁₀)alkyl;linear or branched amino(C₁-C₁₀)alkyl; and substituted or unsubstitutedphenyl.
 4. The method of claim 1 wherein the one or more bisepoxides arechosen from compounds having formula:

wherein R₄ and R₅ may be the same or different and are chosen fromhydrogen and (C₁-C₄)alkyl; R₆ and R₇ may be the same of different andare chosen from hydrogen, methyl and hydroxyl; m=1-6 and n=1-20.
 5. Themethod of claim 1, wherein the one or more halobenzyls have a formula:

wherein R₈, R₉, R₁₀, R₁₁, R₁₂ and R₁₃ are independently chosen fromhydrogen, linear or branched (C₁-C₁₀)alkyl halide, and linear orbranched (C₁-C₁₀)alkyl with the proviso that at least two of R₈, R₉,R₁₀, R₁₁, R₁₂ and R₁₃ are alkyl halide in the same instance and with theproviso that R₆, R₁₀, and R₁₂, or R₉, R₁₁ and R₁₃ are not methyl groupsin the same instance.
 6. The method of claim 1, wherein the reactionproduct is in amounts of 0.25 ppm to 20 ppm.
 7. The method of claim 1,wherein electroplating is done at a current density of 0.25 ASD to 40ASD.
 8. The method of claim 1, wherein the one or more copperphotoresist defined features are pillars, bond pads or line spacefeatures.
 9. An array of photoresist defined features on a substratecomprising an average % TIR of 5% to 10% and a % WID of 8% to 10%.